The present invention relates to tilt correction of a magnet-optical readable medium, and more particularly, to tilt correction method for carrying out tilt correction by detecting crosstalk, magnet-optical reproducing apparatus to be used for practicing the tilt correction method, magnet-optical recording and reproducing apparatus, and magnet-optical readable medium.
As an external memory device for a computer, a magnet-optical disk has great potential. The magnet-optical disk can drastically increase recording capacity in comparison with the flexible disk or hard disk, by forming the recording bits of submicron unit on a medium by application of an external magnetic field and irradiation of a laser beam. For example, the 3.5 inch magnet-optical disk which is at present in practical use has a track of 1.1 .mu.m pitch provided in a radial direction and recording marks of 0.64 .mu.m in the minimum in the circumferential direction, with a recording capacity of approximately 640 MB on one side of the disk.
In order to record further enormous the data amount on such magnet-optical disks and make it possible to record motion images, it is necessary to increase further the recording capacity, i.e., recording density. Thus, it is necessary to shorten the recording mark length and shorten the distance between marks. For that purpose, the wavelength of the laser beam to be irradiated may be shortened, but there has been a problem of lowering the reading signal level. To cope with this problem, there has been proposed a magnetically induced super resolution (MSR) technique to read recording marks smaller in size than the spot diameter by utilizing the temperature distribution in the spot region of the laser beam.
Various MSR media proposed have had problematic points such that a large initializing magnet is required, or though the initializing magnet is not required, the crosstalk is high, or the reading signal level is low, and the like. In this connection, the present applicant proposed in Japanese Patent Application Laid-Open No. 7-244877(1995) an MSR medium with which a transcription region can be formed in a spot by application of low magnetic field, by providing an intermediate layer having specified magnetization characteristics between the reading layer and the recording layer. This MSR medium has resolved the defects of other MSR medium in that it does not necessitate a initialization magnet, it is effective for crosstalk, and can give high reading signal level.
By the way, in recording or reproducing information on a magnet-optical disk, the light beam is irradiated on the magnet-optical disk loaded with an apparatus and the magnetic field is applied. At this time, when the inclination of the magnet-optical disk relative to the light beam (hereinafter to be called tilt) is deviated from a perpendicular line under the loaded state, the recording signal may not be accurately recorded or accurate reading signal may not be obtained. For example, in case of reading the MSR medium proposed by the present applicant as described above, in case a tilt is formed, the temperature distribution in the laser beam spots shows change from the normal state to cause a change in the configuration of the transcription region in the spot. As a result, there has been a problem that the reading signal cannot be obtained in sufficient amplitude.
Furthermore, in the recording of the MSR medium as mentioned above, in case of the formation of tilt, the laser beam power is required to be elevated so as to focus the laser beam, thereby narrowing the recording power margin and providing no practical result.